In communications networks, information may be forwarded from one device to another through intermediate forwarding devices, such as switches. In some networks, links connecting the forwarding devices may serve to arrange the forwarding devices into a topology. The topology defines the overall arrangement of forwarding devices with respect to each other, and the connections between forwarding devices or groups of forwarding devices. In other words, the network topology describes which forwarding devices connect to which other forwarding devices in the network, thereby defining the structure or geometry of the network.
Different types of network topologies may be used, such as grid, torus, interconnect, and Clos topologies. Each type of topology may have advantages and disadvantages for different applications. For example, multi-stage Clos topologies are often employed in data center networks in order to provide full bandwidth connectivity between pairs of servers. FIG. 1 depicts an example of a Clos-style network.
In the network 100, hosts 110 send information to each other through forwarding devices 120. The hosts 110 may be, for example, computers, mobile phones, tablets, servers, or any other suitable device for sending and/or receiving information. The forwarding devices 120 may represent, for example, switches or any other suitable device for forwarding information to or from a device, such as a host 110 or another forwarding device 120.
In a Clos topology, the forwarding devices 120 may be arranged into two or more stages or hierarchical layers 130, 140, 150. In exemplary Clos topologies, the stages may be defined such that a device at a given stage is connected to some or all of the devices at the next stage. In some cases, the devices may be separated into blocks 160 such that connections between two stages (such as the first stage 130 and the second stage 140 in FIG. 1) are made within the block, but not directly between blocks at the stages in question.
Connections between blocks may be provided by devices at higher hierarchical levels. In the example of FIG. 1, the blocks between the first stage 130 and the second stage 140 are connected to each other via high-level forwarding devices 152, 154 at a third stage 150 of the hierarchy. The third stage 150 forwarding devices may be, for example, switches collectively delivering full bisection bandwidth between the second stage 140 forwarding devices.
A Clos arrangement may result in a great deal of interconnectedness within a block 160, such as the blocks connecting stages 1 and 2 in FIG. 1.
One disadvantage of a Clos topology is the relatively high expense of this arrangement. At high levels of the hierarchy (e.g., the third stage 150 in FIG. 1), the forwarding devices 152, 154 must handle large amounts of traffic and are therefore typically complex and expensive devices.